1. Field
The invention relates generally to the art of sterilization and more particularly to the control of temperature in sterilizer chambers.
2. State of the Art
Apparatus for sterilization is used in medical, dental and other institutional settings. Both steam sterilization and chemical sterilization procedures have been developed. Accurate temperature control is needed for both types of sterilization procedures.
In typical prior art sterilizers, the heat source is controlled in a digital fashion in response to the chamber temperature. The heat source is either on, in which case heat is generated to the chamber at a constant rate, or off. When the chamber temperature falls below the desired temperature, the heat source is turned on, and when the chamber temperature exceeds the desired temperature, the heat source is turned off. This type of on/off control is very simple. However, the inherent lags in heat transfer cause considerable oscillation of the actual chamber temperature around the set temperature when such on/off control is used.
An alternate type of temperature control device varies the rate of heat transfer in response to the sensed temperature. When electric heaters are relied upon as the heat source, the input voltage to the heaters may be varied to in turn vary their heat outputs. Where the heat source is steam injected from a steam source, the flow rate of steam can be varied. However, devices employing variable heat transfer require more sophisticated hardware, and are substantially more complicated and expensive than on/off control systems.
The placement of temperature sensors also affects the performance of a heat control system. During a steam cycle, the chamber is filled with saturated steam and the temperature is uniform throughout the chamber. Thus, a sensor anywhere in the chamber will provide an accurate reading for purposes of temperature control. However, while the chamber is being warmed up prior to a cycle, or during a chemical cycle, the chamber vapor is not saturated and the temperature can vary in different parts of the chamber. In the latter case, a single sensor within the chamber will not provide accurate information for temperature control.
Thus, a need remains for sterilization apparatus having simple and inexpensive control of heating which provides accurate temperature control with a minimum of temperature oscillation. There further remains a need for such apparatus which is capable of precise temperature control for both steam and chemical cycles.